BIRDS OF THE ST. CROIX RIVER VALLEY 



105 



stream banks. Tree swallows have benefited by exploiting the large number 

 of eastern bluebird houses that have been placed in agricultural areas and 

 near residential areas. 



Bank Swallow {Riparia riparia) 



Status: Regular migrant and nesting species. 



Migration: Common spring and fall migrant throughout the Valley. Spring 

 migrants arrive in the Western Upland 15-20 April and reach the Northern 

 Highland 20-25 April. Peak abundance occurs between 25 April and 

 15 May. Fall migration begins during mid- July. Peak abundance through 

 the Valley occurs between 25 July and 5 August, and departure by 5 Sep- 

 tember. 



Nesting Season Distribution: Common nesting species throughout the 

 Western Upland and Central Plain becoming uncommon to rare and local in 

 the Northern Highland. Breeding Bird Survey data (Table 3) show that the 

 breeding distribution of this swallow is restricted primarily to areas that are 

 not heavily forested. 



Habitat: Breeding bank swallows are associated with natural banks along 

 rivers, streams, and lakes. Gravel pits and roadside banks that were exposed 

 during highway construction are also heavily used. Colonies are frequently 

 associated with open agricultural areas that are used extensively for for- 

 aging. 



Rough-winged Swallow (Stelgidopteryx ruficollis) 

 Status: Regular migrant and nesting species. 



Migration: Common migrant in the Western Upland and Central Plain, 

 north to Grantsburg, Burnett County; rare and local elsewhere. Spring 

 migrants arrive 15-25 April and peak abundance occurs 25 April to 5 May. 

 Fall migration begins in late July with gathering of family groups. Peak 

 abundance occurs between 25 July and 10 August and departure by 1 Sep- 

 tember. 



Nesting Season Distribution: Fairly common (locally abundant) breeding 

 species in the Western Upland and Central Plain, rare to absent in heavily 

 forested regions. Breeding Bird Survey data suggest that this species is the 

 least common of the swallows nesting in the Valley. However, Goddard 

 (1972) found rough-winged swallows among the 10 most abundant breeding 

 bird species along the Kinnickinnic River, Pierce County. Average breeding 

 density in that area was 26.5 pairs per 40 ha. This exceptionally high density 

 results from the numerous exposed limestone cliffs along that river, which 

 provide abundant nesting sites. 



Habitat: Breeding rough-winged swallows are usually associated with ex- 

 posed banks along rivers and streams. Particularly important are limestone 

 cliffs along fast-moving streams and rivers in the Western Upland. Occa- 

 sional use is made of artificial earthen banks and bridges over small streams. 



